Two major research reports into air pollution have found that is it harming unborn children and that because of climate change it will lead to the premature deaths of thousands more people.

The first report, based on a Queensland study, has found that expectant mothers living in polluted areas of Brisbane are more likely to deliver low weight babies - a major predictor of low IQ and future health problems like cardiovascular disease.

The second report, from Stanford University in the US, has for the first time identified a direct link between increased levels of carbon dioxide in the atmosphere and increased levels of human mortality.

Moreover the Stanford report - based on "state-of-the-art computer modelling" - predicts that for every degree CO2 emissions cause the world's temperature to rise, "upwards of 20,000" more people will die each year worldwide from air pollution.

"This is a cause and effect relationship, not just a correlation," said Professor Mark Jacobson who led the research which is to be published in Geophysical Research Letters.

"The study is the first specifically to isolate carbon dioxide's effect from that of other global-warming agents and to find quantitatively that chemical and meteorological changes due to carbon dioxide itself increase mortality due to increased ozone, particles and carcinogens in the air."

Both the Queensland and the Stanford reports can be expected to increase the pressure for stricter controls on vehicle pollution.

In fact the Stanford report comes just at a time when in the US California's State Government is about to face a court battle with the federal Environment Protection Agency (EPA) over whether California can go it alone and introduce stricter anti-pollution laws.

Until now one of EPA's the prime arguments against California drawing up its own State laws to control vehicle emissions has been that there is no research to suggest that CO2 emissions on their own are a threat to health.

The latest Stanford research not only shows that CO2 is a culprit but that California of all US States will suffer the most because of rising levels of CO2.

The Queensland report, published in the international journal Environmental Health Perspectives, is also likely to put pressure on governments around Australia to take action to cut air pollution - including CO2.

It was based on the work of senior research fellow Dr Adrian Barnett of Queensland University of Technology.

He and his research team spent ten years studying ultrasound scans taken of 15,000 foetuses.

Each foetus was being carried by a woman who was living within 14km of the centre of Brisbane.

Each scan was assessed for the size and age of the foetus and compared with the known levels of air pollution where the mother was living.

"The study found that mothers with a higher exposure to air pollution had foetuses that were, on average, smaller in terms of abdominal circumference, head circumference and femur length," Dr Barnett said.

He said the study looked at foetuses of between 13 and 26 weeks duration.

"To our knowledge this is the first study of its kind as it uses ultrasound measurement as a direct estimate of growth, rather than using birth weight as a delayed measure of growth," Dr Barnett said.

Dr Barnett said it was wise for pregnant women to try to reduce their exposure to air pollution, most of which in Brisbane was caused by vehicles.

"While we need to get more data from individual mothers before we can be more certain about the effects of air pollution on foetal development, we would recommend that where possible pregnant women reduce their exposure to air pollution."